1. Field of the Invention
The present invention generally relates to data-management devices and data-management methods such as databases, and particularly relates to a data-management device and a data-management method which determine a data structure while storing data.
2. Description of the Related Art
Data-management methods used in databases and the like include a relation-type data-management method expressing relations between objects by using tables and a network-type data-management method linking each object by representing relations between objects by using links. These two methods are those most commonly used in the field. In data-management devices using these data-management methods, a schema (information about a data structure of stored data) should be decided first, and, then, values of data are stored based on the determined data structure. Namely, a schema must be decided by estimating usage of stored data prior to the development of databases.
In data-management devices utilizing an object-oriented scheme, objects can inherit attributes from more general objects. Based on this inheritance relation, data can be organized by grouping objects of upper-level concepts and objects of lower-level concepts together. Thus, data management can be efficiently carried out. Even in such data-management devices employing the object-oriented scheme, values of each data can be stored only after a data structure of objects representing concepts is determined.
In these data-management devices, there is a problem in that it is difficult to modify the data structure once it is determined. For example, when usage of a database is changed in response to changes in an environment in which the database is used, it is desirable to continue to use the existing data structure for a new demand. But the existing data structure without modification cannot be applicable in the new environment. Namely, the data-management device cannot satisfy a need of users when the users want an expansion of the database beyond an existing framework. In order to expand and modify the database beyond the existing framework, modification of the data structure, reentry of all values, development of application programs, etc., must be accomplished, taking a long time.
Furthermore, in the data-management devices based on the object-oriented scheme, there is a case in which a gap develops between concepts represented by objects and values to be stored, as the values of data are accumulated in the databases. Namely, as the values are accumulated after deciding on a data structure representing concepts from upper levels to lower levels, a new data structure may become necessary to represent new concepts, or concepts based on the existing data structure may be required to be modified. In this case, the data-management devices of the related art need reentry of all the data after newly developing a data structure representing the upper-level concepts.
Accordingly, there is a need in the field of data-management devices and data-management methods for a data-management device and a data-management method which can determine a data structure during the accumulation of values when a determination of the data structure is difficult prior to the collection of actual values or when the usage of the values frequently varies, and, further, which can change the data structure according to the usage of the values.
Also, there is a need for a data-management device and a data-management method which can use values without any change for applications developed in consistency with the original data structure even when the data structure is changed, and, further, which can cope with the newly added data structure by allowing development of additional applications.
Also, there is a need for a data-management device and a data-management method which can create an appropriate data structure matching with the usage of values by uncovering relations between the values during the accumulation of the values.